Voice interface for a search engine

ABSTRACT

A system provides search results from a voice search query. The system receives a voice search query from a user, derives one or more recognition hypotheses, each being associated with a weight, from the voice search query, and constructs a weighted boolean query using the recognition hypotheses. The system then provides the weighted boolean query to a search system and provides the results of the search system to a user.

FIELD OF THE INVENTION

The present invention relates generally to information retrieval systemsand, more particularly, to a system and method for supporting voicequeries in information retrieval systems.

BACKGROUND OF THE INVENTION

To satisfy the average user, a voice interface to a search engine mustrecognize spoken queries, and must return highly relevant searchresults. Several problems exist in designing satisfactory voiceinterfaces. Current speech recognition technology has high word errorrates for large vocabulary sizes. There is very little repetition inqueries, providing little information that could be used to guide thespeech recognizer. In other speech recognition applications, therecognizer can use context, such as a dialogue history, to set upcertain expectations and guide the recognition. Voice search querieslack such context. Voice queries can be very short (on the order of onlya few words or single word), so there is very little information in theutterance itself upon which to make a voice recognition determination.

Current voice interfaces to search engines address the above problems bylimiting the scope of the voice queries to a very narrow range. At everyturn, the user is prompted to select from a small number of choices. Forexample, at the initial menu, the user might be able to choose from“news,” “stocks,” “weather,” or “sports.” After the user chooses onecategory, the system offers another small set of choices. By limitingthe number of possible utterances at every turn, the difficulty of thespeech recognition task is reduced to a level where high accuracy can beachieved. This approach results in an interactive voice system that hasa number of severe deficiencies. It is slow to use, since the user mustnavigate through may levels of voice menus. If the user's informationneed does not match a predefined category, then it becomes verydifficult or impossible to find the information desired. Moreover, it isoften frustrating to use, since the user must adapt his/her interactionsto the rigid, mechanical structure of the system.

Therefore, there exists a need for a voice interface that is effectivefor search engines.

SUMMARY OF THE INVENTION

A system and method consistent with the present invention address thisand other needs by providing a voice interface for search engines thatis capable of returning highly relevant results.

In accordance with the purpose of the invention as embodied and broadlydescribed herein, a method that provides search results includesreceiving a voice search query from a user; deriving one or morerecognition hypotheses from the voice search query, each recognitionhypothesis being associated with a weight; constructing a weightedboolean query using the recognition hypotheses; providing the weightedboolean query to a search system; and providing results of the searchsystem.

In another implementation consistent with the present invention, aserver includes a memory and a processor. The processor receives one ormore recognition hypotheses. The recognition hypotheses are constructedfrom a voice search query. The processor also determines the length ofthe shortest recognition hypothesis, prunes the length of eachrecognition hypothesis up to the length of the shortest recognitionhypothesis, determines a length of a longest pruned recognitionhypothesis, selects a number of recognition hypotheses based on a valuerepresenting the length of the longest recognition hypothesis,determines query term weights, and forms a weighted boolean query out ofeach word position in the selected recognition hypotheses.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate an embodiment of the inventionand, together with the description, explain the invention. In thedrawings,

FIG. 1 illustrates an exemplary network in which a system and method,consistent with the present invention, may be implemented;

FIG. 2 illustrates an exemplary client device consistent with thepresent invention;

FIG. 3 illustrates an exemplary server consistent with the presentinvention;

FIG. 4 illustrates an exemplary process, consistent with the presentinvention, for producing models for use in voice-based searching;

FIG. 5 illustrates an exemplary process, consistent with the presentinvention, for performing a search;

FIGS. 6A and 6B illustrate an exemplary n-best hypothesis list and aword graph, respectively, consistent with the present invention; and

FIG. 7 illustrates an exemplary process, consistent with the presentinvention, for constructing a search query.

DETAILED DESCRIPTION

The following detailed description of the invention refers to theaccompanying drawings. The same reference numbers in different drawingsidentify the same or similar elements. Also, the following detaileddescription does not limit the invention. Instead, the scope of theinvention is defined by the appended claims.

Implementations consistent with the present invention provide a voiceinterface to search engines. In response to a voice query, a serverautomatically constructs a search query to cover the most likelyhypotheses identified by a speech recognizer.

Exemplary Network

FIG. 1 illustrates an exemplary network 100 in which a system andmethod, consistent with the present invention, may be implemented. Thenetwork 100 may include multiple client devices 110 connected tomultiple servers 120–130 via a network 140. The network 140 may includea local area network (LAN), a wide area network (WAN), a telephonenetwork, such as the Public Switched Telephone Network (PSTN), anintranet, the Internet, or a combination of networks. Two client devices110 and three servers 120–130 have been illustrated as connected tonetwork 140 for simplicity. In practice, there may be more or lessclient devices and servers. Also, in some instances, a client device mayperform the functions of a server and a server may perform the functionsof a client device.

The client devices 110 may include devices, such as mainframes,minicomputers, personal computers, laptops, personal digital assistants,telephones, or the like, capable of connecting to the network 140. Theclient devices 110 may transmit data over the network 140 or receivedata from the network 140 via a wired, wireless, or optical connection.

The servers 120–130 may include one or more types of computer systems,such as a mainframe, minicomputer, or personal computer, capable ofconnecting to the network 140 to enable servers 120–130 to communicatewith the client devices 110. In alternative implementations, the servers120–130 may include mechanisms for directly connecting to one or moreclient devices 110. The servers 120–130 may transmit data over network140 or receive data from the network 140 via a wired, wireless, oroptical connection.

In an implementation consistent with the present invention, the server120 may include a search engine 125 usable by the client devices 110.The servers 130 may store documents, such as web pages, accessible bythe client devices 110.

Exemplary Client Architecture

FIG. 2 illustrates an exemplary client device 110 consistent with thepresent invention. The client device 110 may include a bus 210, aprocessor 220, a main memory 230, a read only memory (ROM) 240, astorage device 250, an input device 260, an output device 270, and acommunication interface 280. The bus 210 may include one or moreconventional buses that permit communication among the components of theclient device 110.

The processor 220 may include any type of conventional processor ormicroprocessor that interprets and executes instructions. The mainmemory 230 may include a random access memory (RAM) or another type ofdynamic storage device that stores information and instructions forexecution by the processor 220. The ROM 240 may include a conventionalROM device or another type of static storage device that stores staticinformation and instructions for use by the processor 220. The storagedevice 250 may include a magnetic and/or optical recording medium andits corresponding drive.

The input device 260 may include one or more conventional mechanismsthat permit a user to input information to the client device 110, suchas a keyboard, a mouse, a pen, a microphone, voice recognition and/orbiometric mechanisms, etc. The output device 270 may include one or moreconventional mechanisms that output information to the user, including adisplay, a printer, a speaker, etc. The communication interface 280 mayinclude any transceiver-like mechanism that enables the client device110 to communicate with other devices and/or systems. For example, thecommunication interface 280 may include mechanisms for communicatingwith another device or system via a network, such as network 140.

As will be described in detail below, the client devices 110, consistentwith the present invention, perform certain searching-relatedoperations. The client devices 110 may perform these operations inresponse to processor 220 executing software instructions contained in acomputer-readable medium, such as memory 230. A computer-readable mediummay be defined as one or more memory devices and/or carrier waves.

The software instructions may be read into memory 230 from anothercomputer-readable medium, such as the data storage device 250, or fromanother device via the communication interface 280. The softwareinstructions contained in memory 230 causes processor 220 to perform thesearch-related activities described below. Alternatively, hardwiredcircuitry may be used in place of or in combination with softwareinstructions to implement processes consistent with the presentinvention. Thus, the present invention is not limited to any specificcombination of hardware circuitry and software.

Exemplary Server

FIG. 3 illustrates an exemplary server 120 consistent with the presentinvention. Server 130 may be similarly configured. The server 120includes a bus 310, a processor 320, a memory 330, an input device 340,an output device 350, and a communication interface 360. The bus 310 mayinclude one or more conventional buses that allow communication amongthe components of the server 120.

The processor 320 may include any type of conventional processor ormicroprocessor that interprets and executes instructions. The memory 330may include a RAM or another type of dynamic storage device that storesinformation and instructions for execution by the processor 320; a ROMor another type of static storage device that stores static informationand instructions for use by the processor 320; and/or some type ofmagnetic or optical recording medium and its corresponding drive.

The input device 340 may include one or more conventional devices thatpermits an operator to input information to the server 120, such as akeyboard, a mouse, a pen, a microphone, voice recognition and/orbiometric mechanisms, and the like. The output device 350 may includeone or more conventional devices that outputs information to theoperator, including a display, a printer, a speaker, etc. Thecommunication interface 360 may include any transceiver-like mechanismthat enables the server 120 to communicate with other devices and/orsystems. For example, the communication interface 360 may includemechanisms for communicating with other servers 130 or the clientdevices 110 via a network, such as network 140.

Execution of the sequences of instructions contained in memory 330causes processor 320 to perform the functions described below. Inalternative embodiments, hardwired circuitry may be used in place of orin combination with software instructions to implement the presentinvention. Thus, the present invention is not limited to any specificcombination of hardware circuitry and software.

Exemplary Processing

FIG. 4 illustrates an exemplary process, consistent with the presentinvention, for producing models for use in voice-based searching. In animplementation consistent with the present invention, a server, such asserver 120, may perform this process. It will be appreciated, however,that a client device 110 may alternatively perform the entire process orpart of the process described below.

Processing may begin with the server 120 receiving search query logs(i.e., one or more previously executed queries) [act 405]. The querylogs may consist of audio data (i.e., a recorded query) and/or a textualtranscription of the audio data. The textual transcription may beobtained manually or, as will be described in more detail below, may beautomatically performed by the server 120. The query logs may alsoconsist of typed query logs from, for example, a text-based searchengine.

The server 120 may filter the query log to remove unwanted data [act410]. The server 120 may filter the query log by language (e.g.,English, French, Spanish, etc.), filter out misspelled words, filter outbad audio data, and/or filter out words that are not desirable.

The server 120 may then perform statistical analysis on the query log[act 415]. The server 120 may, for example, determine the most frequentqueries, the most frequent words, the number of frequent words thatcover a certain proportion of queries or query words, etc. The server120 may also construct statistical language models 420 by counting theoccurrence of words in certain contexts, smoothing the counts to obtainbetter probability estimates, and pruning the models to obtain asatisfactory size/effectiveness tradeoff. Language models 420 may beconstructed for different users or different user groups. For example,the server 120 may construct a language model 420 for a user groupconsisting of English speakers with German accents and a differentlanguage model for a user group consisting of English speakers withFrench accents. As illustrated in FIG. 4, the statistical analysisprocess also produces a vocabulary 425. The vocabulary 425 provides alist of words and word compounds (i.e., words that commonly occurtogether) to be used during the speech recognition process describedbelow.

The server 120 may phonetically transcribe the words in the vocabulary425 [act 430]. Here, the server 120 may associate one or more phonetictranscriptions with each word in the vocabulary 425. This phonetictranscription may be performed manually or automatically by the server120. As a result of performing the phonetic transcription, the server120 produces a phonetic dictionary 435. The phonetic dictionary 435associates a list of words (and compounds) with possible pronunciations.

In response to receiving the query logs [act 405], the server 120 mayalso perform acoustic training by recording actual audio samples [act440]. These audio samples may be used to train acoustic models 445 thatwill be later used to aid in the speech recognition process. The server120 may then store the language models 420, phonetic dictionary 435, andacoustic models 445 in memory [act 450]. The server 120 may, forexample, store the language models 420, phonetic dictionary 435, andacoustic models 445 locally at the server 120 (e.g., in memory 330) orexternally from the server 120.

The server 120 may perform the processing described above a single timeor at predetermined times. For example, the server 120 may update thelanguage models 420, phonetic dictionary 435, and acoustic models 445 atpredetermined time intervals (e.g., every hour) or as new query logs arecreated.

FIG. 5 illustrates an exemplary process, consistent with the presentinvention, for performing a search. While the foregoing acts aredescribed as being performed by a server, it will be appreciated that aclient device may alternatively perform some of the acts describedbelow.

Processing may begin with a server, such as server 120, receiving avoice query [act 505]. The voice query may be received via the server's120 input device 340 or over the network 140 via a separate device, suchas a client device 110.

The server 120 may process the received voice query in a well-knownmanner to form a digital audio signal [act 510]. For example, the server120 may perform analog-to-digital conversion to convert the audio signalto digital form and may break the digital audio signal into shortwindows (e.g., 10–20 ms frames). In an implementation consistent withthe present invention, the server 120 may also determine which languagemodel 420 is best suited for this voice query. For example, the server120 may determine that a language model 420 directed to English speakerswith German accents is best suited for this query.

The server 120 may then perform acoustic feature extraction in awell-known manner [act 515]. Within each of the short windows, theserver 120 may look for acoustic features to identify the sound that wasspoken, derive a short feature vector, and classify the feature vectorinto a small number of categories.

The server 120 may perform speech recognition processing in a well-knownmanner on the feature vectors to derive word hypotheses [act 520]. Theserver 120 may analyze the feature vectors using the phonetic dictionary435 that links one or more acoustic representations to words, thelanguage model 420 to assign a probability value to different possiblesequences of what could have been spoken, and acoustic models 445 tomatch the sequence of feature vectors with actual sound units. Thespeech recognition processing results in a list of the n-best wordhypotheses and/or a word graph 525.

In an implementation consistent with the present invention, the server120 may associate a weight with each possible word or word combination.The server 120 may determine these weights from confidence scores fromthe speech recognition processing, a priori probability from thelanguage model, or, as will be described in more detail below, thenumber of documents resulting from a search or the frequency of thewords/compounds in the resulting documents. Alternatively, the server120 may use a combination of these techniques for determining weights.

Assume, for example, that a user wanted to search for informationrelating to the White House. Upon receiving the voice query, the server120 may determine that the user query contained the following possiblewords “white,” “light,” “house,” and “mouse.” FIGS. 6A and 6B illustratean exemplary n-best hypothesis list 600 and a word graph 650,respectively, that may be produced by the server 120. As illustrated inFIG. 6A, the n-best hypothesis list 600 may contain a list of possiblewords or word-combinations that may be included in the voice query,along with associated weights. For example, the server 120 may determinethat the voice query contains the word combinations “white house,”“light house,” “white mouse,” or “light mouse” and may associate weightsof 0.8, 0.73, 0.6, and 0.35, respectively, with these word combinations.

Alternatively, the server 120 may, as illustrated in FIG. 6B, produce aword graph 650 containing all word combination possibilities withassociated weights. As illustrated, the server 120 may associate aweight of 0.8 with the word “white,” a weight of 0.7 with the word“house,” a weight of 0.5 with the word “light,” and a weight of 0.4 withthe word “mouse.” As described above, the server 120 may determine theseweights from confidence scores from the speech recognition processing, apriori probability from the language model, or search results.

The server 120 may set a group of query constraint parameters 530. Theseparameters may include the number of hypotheses to be considered (T),the total number of words to be included in a query (WordLimit), and theproportion of new words added from a first query possibility to a nextquery possibility (ProportionNewWords). These parameters may beautomatically set by the server 120 or may be set manually. Moreover,these parameters may vary by user or user group.

Using the query constraint parameters 530 and the query term weights532, the server 120 may construct a search query from the hypothesislist or word graph [act 535]. The server 120 may construct the searchquery to cover all (or the most likely) possible hypotheses. FIG. 7illustrates an exemplary process, consistent with the present invention,for constructing a search query. Assume in act 520 that the server 120produces an n-best hypothesis list 525. Using the hypothesis list 525,the server 120 may determine the length (MinLen) of the shortesthypothesis within the top hypotheses [act 710].

The server 120 may then remove noise words, such as “the,” “of,” “for,”etc., that were incorrectly inserted by the server 120 during the speechrecognition process to prune each hypothesis up to the length MinLen[act 720]. The server 120 may determine the length (MaxLen) of thelongest pruned hypothesis [act 730]. The server 120 may, for example,determine MaxLen via a comparison operation. The server 120 may select khypotheses from the n-best hypothesis list 525 [act 740], where

$k = {1 + {\frac{{WordLimit} - {MaxLen}}{{MaxLen}*{ProportionNewWords}}.}}$

The server 120 may then obtain the weights 532 for the selectedhypotheses [act 750]. The server 120 may form a weighted boolean query[act 760]. For the example above, the server 120 may produce thefollowing boolean query:

-   -   0.8(white house) OR 0.73(light house) OR 0.6(white mouse) OR        0.35(light mouse).

Alternatively, the server 120 may produce the following query:

$\begin{pmatrix}{0.8\mspace{14mu}{white}} \\{OR} \\{0.5\mspace{14mu}{light}}\end{pmatrix}\mspace{14mu}{AND}\mspace{14mu}{\begin{pmatrix}{0.7\mspace{14mu}{house}} \\{OR} \\{0.4\mspace{14mu}{mouse}}\end{pmatrix}.}$

In forming the boolean search query, terms may be repeated if necessary.For example, assume that the server 120 produces the followinghypothesis list:

-   -   AB    -   CDE    -   FGH.

Assuming that each of these hypotheses is weighted equally, the server120 may produce the following search query based on this hypothesislist:

$\begin{pmatrix}A \\{OR} \\C \\{OR} \\F\end{pmatrix}\mspace{14mu}{AND}\mspace{14mu}\begin{pmatrix}B \\{OR} \\D \\{OR} \\G\end{pmatrix}\mspace{14mu}{AND}\mspace{14mu}{\begin{pmatrix}B \\{OR} \\E \\{OR} \\H\end{pmatrix}.}$

Since the first hypothesis (AB) includes fewer terms than the otherhypotheses, the server 120 may reuse one of the terms from the firsthypothesis.

Once the weighted search query has been formed, the server 120 may,through the use of the search engine 125, perform a search using thequery via any conventional technique [act 540]. The server 120 may thentailor the search results based on the query term weights 532. Forexample, the query term weights 532 may be provided as an input to thesearch engine 125 along with the query terms. The search engine 125could use the query term weights 532 to determine how to rank the searchresults. For the example above, the search engine 125 may boost theranking of a search result that contains “white house” compared to onethat contains “light mouse,” since “white house” is weighted moreheavily.

The server 120 may also use the query term weights to filter (ororganize) the search results obtained by the search engine 125. Forexample, suppose the search engine 125 normally displays 10 searchresults per query. The server 120 may use the relative weights of thedifferent hypotheses/terms to ensure that the first 10 results containresults that are proportional to the relative weights. As an example,the relative weight associated with “white house” in FIG. 6A is 0.32(i.e., 0.8/2.48), and the relative weight of “light mouse” is 0.14(0.35/2.48). Using these weights, the server 120 could filter the searchresults so that 3.2 (rounded to 3) of the first 10 search results arerelate to “white house” and 1.4 (rounded to 1) of the results relate to“light mouse.” Furthermore, it may be desirable to list the “whitehouse” search results before the “light mouse” search results due to itshigher relative weight. It will be appreciated that other ways offiltering search results using the query term weights may alternativelybe used.

In another implementation consistent with the present invention, theserver 120 may use the query term weights to eliminate (i.e., not use aspart of the search query) hypotheses or terms that have aweight/confidence score below a predefined threshold value. For example,assume that the threshold was set such that hypotheses with a weight 0.4or below should be eliminated. For the hypothesis list provided abovewith respect to FIG. 6A, the server 120 may eliminate the hypothesis“light mouse” since it is associated with a weight below the thresholdvalue of 0.4.

Once the search results have been obtained, the server 120 may use thesesearch results to refine the search query. For example, assume that theserver 120 constructs a boolean search query using the hypotheses listedin FIG. 6A. Assume further that none of the documents obtained by thesearch engine 125 correspond to the hypothesis “light mouse.” In such acase, the server 120 may discard that hypothesis from the original list,create a new boolean search query using the remaining hypotheses, andthen perform a search using the new search query. The server 120 mayperform this iteration once, or repeatedly until, for example, each ofthe hypotheses has search results associated with it.

As an alternative to deleting a hypothesis if there are no correspondingsearch results, the server 120 may modify the weights (confidencescores) of those hypotheses based on the contents of the documentscorresponding to the search results. Here, the server 120 may, forexample, increase the weights associated with those hypotheses or termsrelating to a high number of results.

In yet a further implementation consistent with the present invention,the server 120 may consider compounds in performing or refining thesearch. In some conventional searching techniques, a search engine mayobtain better results for the compound “new york restaurants” than thesearch engine would return if the terms “new,” “york,” and “restaurants”were separately entered. According to this exemplary implementation, theserver 120 may develop the n-best hypothesis list 525, feed it into asearch engine 125, evaluate the search results to identify compounds,and revise the hypothesis list based on the identified compounds. As analternative to identifying compounds after receiving search results, theserver 120 may detect compounds prior to constructing the search query535. In such a situation, the server 120 may then replace an existinghypothesis with the compound when constructing the search query.

Once the search results have been obtained, the server 120 may thenprovide the results to the user via the client 110 [act 545]. The server120 may, for example, cause the results to be displayed to the user.

CONCLUSION

A system and method consistent with the present invention provide avoice interface for search engines. Through the use of a language model,phonetic dictionary, and acoustic models, a server generates an n-besthypothesis list or word graph. The server uses the n-best hypothesislist or word graph to construct a search query to cover possiblepossibilities. As a result, the server is capable of returning relevantsearch results for even queries containing few words.

The foregoing description of exemplary embodiments of the presentinvention provides illustration and description, but is not intended tobe exhaustive or to limit the invention to the precise form disclosed.Modifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention. Forexample, while series of acts have been presented with respect to FIGS.5 and 7, the order of the acts may be altered in other implementationsconsistent with the present invention. No element, act, or instructionused in the description of the present application should be construedas critical or essential to the invention unless explicitly described assuch.

The scope of the invention is defined by the following claims and theirequivalents.

1. A method for providing search results, comprising: receiving a voicesearch query from a user; deriving one or more recognition hypothesesfrom the voice search query, each recognition hypothesis beingassociated with a weight and including one or more terms; constructing aweighted boolean query using the recognition hypotheses, theconstructing including: determining a length of a shortest recognitionhypothesis, pruning a length of each recognition hypothesis up to thelength of the shortest recognition hypothesis, determining a length of alongest pruned recognition hypothesis, selecting a number of recognitionhypotheses based on one or more query parameters, determining termweights, and forming a weighted boolean query; providing the weightedboolean query to a search system; and providing results of the searchsystem.
 2. The method of claim 1 wherein the deriving one or morerecognition hypotheses includes: using one or more of a language model,phonetic dictionary, or acoustic models to derive the recognitionhypotheses.
 3. The method of claim 2 further comprising: updating one ormore of the language model, phonetic dictionary, or acoustic modelsusing the voice search query.
 4. The method of claim 1 furthercomprising: identifying a language model based on at least onecharacteristic associated with the user, and wherein the deriving one ormore recognition hypotheses includes: using the identified languagemodel to derive the one or more recognition hypotheses.
 5. The method ofclaim 1 wherein the query parameters include the determined length ofthe longest pruned recognition hypothesis, a value representing a totalnumber of terms to be included in a query, and a value representing aproportion of new terms added from a first recognition hypothesis to asecond recognition hypothesis.
 6. The method of claim 1 wherein thequery parameters vary by user or user group.
 7. The method of claim 1wherein the providing results of the search system includes: adjusting aranking of the results of the search system based on the weights.
 8. Themethod of claim 1 wherein the providing results of the search systemincludes: organizing the results based on the weights.
 9. The method ofclaim 1 further comprising: discarding, prior to constructing theweighted boolean query, those recognition hypotheses associated with aweight below a threshold value.
 10. The method of claim 1 wherein theweighted boolean query is a weighted OR-query.
 11. The method of claim 1further comprising: refining the weighted boolean query based on theresults of the search system.
 12. The method of claim 11 wherein therefining includes: determining a quantity of results related to eachrecognition hypothesis, and discarding recognition hypotheses having noresults.
 13. The method of claim 11 wherein the refining includes:determining a quantity of results related to each recognitionhypothesis, and adjusting the weight associated with the recognitionhypothesis based on the quantity.
 14. The method of claim 1 furthercomprising: detecting compounds in the one or more recognitionhypotheses, and wherein the constructing a weighted boolean queryincludes: constructing the weighted boolean query using the recognitionhypotheses and the detected compounds.
 15. The method of claim 1 furthercomprising: detecting compounds in the results of the search system;refining the weighted boolean query based on the detected compounds;providing the refined weighted boolean query to the search system; andproviding the new results.
 16. A method for generating a search query,comprising: receiving one or more recognition hypotheses, eachrecognition hypothesis being constructed from a voice search query;determining a length of a shortest recognition hypothesis; pruning alength of each recognition hypothesis up to the length of the shortestrecognition hypothesis; determining a length of a longest prunedrecognition hypothesis; selecting a number of recognition hypothesesbased on the length of the longest pruned recognition hypothesis;determining query term weights; and forming a weighted boolean query outof each term position in the selected recognition hypotheses.
 17. Themethod of claim 16 wherein the pruning includes: removing noise wordsfrom the recognition hypotheses.
 18. The method of claim 16 wherein theselecting includes: identifying a number of recognition hypotheses basedon the determined length of the longest pruned recognition hypothesis, avalue representing a total number of terms to be included in a query,and a value representing a proportion of new terms added from a firstrecognition hypothesis to a second recognition hypothesis.
 19. A servercomprising: a memory configured to store instructions; and a processorconfigured to execute the instructions to receive one or morerecognition hypothesis, each recognition hypothesis being constructedfrom a voice search query, determine a length of a shortest recognitionhypothesis, prune a length of each recognition hypothesis up to thelength of the shortest recognition hypothesis, determine a length of alongest pruned recognition hypothesis, select a number of recognitionhypotheses, the number being based on a value representing the length ofthe longest pruned recognition hypothesis, determine query term weights,and form a weighted boolean query out of each term position in theselected recognition hypotheses.
 20. A computer-readable mediumcontaining instructions for controlling at least one processor toperform a method for generating a search query, comprising: receiving atleast one recognition hypothesis, the recognition hypothesis beingconstructed from a voice search query and having one or more terms;determining a length of a shortest recognition hypothesis; pruning alength of each recognition hypothesis up to the length of the shortestrecognition hypothesis; determining a length of a longest prunedrecognition hypothesis; selecting a number of recognition hypotheses,the number being based on the length of the longest pruned recognitionhypothesis; determining term weights; and forming a weighted booleanquery out of the selected recognition hypotheses.